November 9, 2011

Alkermes plc (NASDAQ: ALKS) today presented positive results from a long-term study of VIVITROL® (naltrexone for extended-release injectable suspension) at the 24th Annual U.S. Psychiatric and Mental Health Congress in Las Vegas, NV. Results from the one-year, open-label extension of the six-month pivotal study showed sustained efficacy of VIVITROL, as measured by the number of opioid-free urine screens, in patients who received VIVITROL, in combination with psychosocial treatment, for a total of 18 months of treatment. Additionally, all safety events observed during the open-label extension were consistent with those set forth in the approved product labeling.

"The robust data from this extension study confirm VIVITROL's efficacy and safety profile over an 18-month period and support its clinical utility as a treatment option for opioid dependence, following opioid detoxification," stated Evgeny Krupitsky, M.D., Ph.D., Professor of Psychiatry, St. Petersburg State Pavlov Medical University and Head of the Department of Addictions at the Bekhterev Research Psychoneurological Institute. "VIVITROL is the first and only once-monthly medication that offers patients and physicians a non-narcotic treatment option to help fight this challenging disease."

During the total observation period of 18 months, improvements during the six-month pivotal trial observed in patients treated with VIVITROL were maintained for the duration of the subsequent one-year, open-label extension study. Half of the patients (49%) who entered the one-year extension study, after receiving six months of VIVITROL in the pivotal study, were completely abstinent for the duration of the extension study, based on opioid-free urine screens. The response profile based on the number of opioid-free urine screens was the primary efficacy endpoint of the six-month pivotal study. The extension study also measured opioid craving, improvements in quality of life measures, self-reported opioid use and incidence of physical opioid dependence, confirming the findings documented in the first phase of the study. All patients received psychosocial counseling.

Treatment with VIVITROL during this study showed a low rate of clinical adverse events, the absence of severe adverse events and a low overall rate (2.6%) of injection site pain, with no serious injection site reactions. All safety events observed during the open-label extension were consistent with those set forth in the approved product labeling. No patients discontinued the open-label extension due to serious adverse events. The most common clinical adverse events listed in the extension study were toothache and influenza.

Overall, nearly 65% of patients completed the open-label study, representing a high completion rate for an addiction study. At the onset of the study, 114 patients from the original six-month pivotal trial continued into the open-label, 52-week extension study. Sixty-seven patients continued treatment with VIVITROL, while 47 patients who had been on placebo crossed over to receive VIVITROL.